When are you most likely to spend the money you have (or wish you had)? You are most likely to spend when you go out. Sometimes you go out with the intention of "just looking". How many times do you end up getting something? Maybe you picked it up because it was on sale. Or because you think it is soooo cool. Or because it would make a great gift. We can usually justify our purchases. The question here, however, is instead "Are we buying a planned purchase?"
Planned purchases (groceries, for instance) are things we have planned for before we go out. Planned purchases are ok, because we’ve had time to think about what we need (or maybe want) and have a valid reason for purchasing ahead of time. A valid reason can be whatever is "valid" for you. Your valid and my valid may be different, and that’s ok. Just know that you’ve taken the time ahead of time to validate your purchase, instead of making it a spur of the moment purchase.
This can also apply to online purchases. Have you ever been looking for something online, and then just start to browse around? Maybe you’ve found something, again, that you really want — but it wasn’t planned. This is the same as going out without a plan. In this case, you’re just going out into cyberspace to do your shopping.
So, think about it the next time you go out. Are you going for with a purpose? Maybe the solution is to not go out at all. Stay home and save! Save up for something you really want or need.